This invention relates to a fluid flow sensor device for providing an indication of the amount of liquid flow through a conduit. More particularly, it relates to such a sensor device adaptable for use in conjunction with an automotive computer for measuring and displaying fuel consumption and related performance data.
In many types of control and measuring apparatus, it is necessary to determine with accuracy, the amount of liquid that is flowing at a given instant. Various forms of such liquid flow sensors have been suggested and developed, such as the type wherein a stream of the liquid is forced to flow through a circular path and causes a ball element to move continuously with the liquid stream around the path so that the speed of the stream and thus, its flow rate per unit time, can be measured. Such flow sensors are typified by the device disclosed in U.S. Pat. No. 3,872,304. Such rotating ball type flow sensors have inherent limitations of accuracy and reliability, particularly at low liquid flow rates. Moreover, such sensors must be mounted so that the ball track is in a horizontal plane in order to maintain its accurate operation. With crowded engine compartments in modern vehicles, this was often a difficult requirement to meet. Also, such prior flow sensors were often subject to internal liquid pressure variations or to vapor on trapped air factors. In internal combustion engines for vehicles where it is desired to measure the flow rate of fuel to determine the rate of fuel composition per distance traveled, such problems were especially serious where the flow sensor was required to measure low liquid flow rates with a relatively high degree of accuracy. The present invention solves this problem.
Another form of fluid flow meter, known as the differential pressure type, normally utilizes a movable element which, in response to variations in flow rate, causes corresponding changes in cross-sectional area of an orifice through which the fluid is flowing. Such flow meters heretofore devised, as shown typically in U.S. Pat. Nos. 4,041,758 and 3,889,535, were relatively complicated in construction, required close tolerance parts and were difficult to calibrate. Also, they were often limited to certain mounting requirements to compensate for gravity effects, or they were subject to internal friction or fluid leakage effects. The present invention provides an improved fluid flow sensor which overcomes such problems.
Another disadvantage with variable area flow sensors heretofore devised was that they were relatively complicated and therefore expensive to manufacture. For example, with such prior sensors, it was necessary to provide a specially contoured needle member for determining the size of the flow passage in combination with an orifice member in order to provide the desired accuracy. To form such a precisely contoured needle element required expensive manufacturing techniques. The present invention solves this problem by providing a flow sensor comprised of elements in combination including a needle element with an easily machined straight taper, and yet a sensor that operates with relatively high accuracy.
It is therefore a general object of the present invention to provide an improved fluid flow sensor of the variable area type that is compact, yet highly accurate, and particularly well adapted for use with a vehicular fuel monitoring system.
Another object of the invention is to provide a flow sensor comprised of components formed from the same or similar materials so that it will function with accuracy despite variations in environmental temperature.
Still another object of the present invention is to provide a fluid flow sensor that is rugged and durable and yet capable of accurate operation despite its orientation in any plane relative to the horizontal.
Yet another object of the invention is to provide a fluid flow sensor that is particularly well adapted for economy of manufacture.